[Haskell-cafe] -XGADTs changes type for program that does not contain GADT

Andres Löh andres at well-typed.com
Fri Feb 12 13:05:12 UTC 2016


> the following type-correct program does not contain GADT syntax.
> When I activate GADT language pragma, it does no longer typecheck.

This is because -XGADTs implies -XMonoLocalBinds. See
https://ghc.haskell.org/trac/ghc/blog/LetGeneralisationInGhc7 for a
longer explanation.


Andres Löh, Haskell Consultant
Well-Typed LLP, http://www.well-typed.com

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